Methods for producing low temperature refrigeration



Aug. 10, 1965 K. ZEITZ ETAL. 3,199,304

METHODS FOR PRODUCING LOW TEMPERATURE REFRIGERATION Filed Jan. 18, 1963 7 Q I5 N 1 INVENTORS KENNETH ZEITZ BY JACOB M. GEIST PETER K. LASHMET ATTORNEY United States Patent 3,199,304 METHQDS FGR PRODUUING LOW TEM- PERATURE REFRIGERATION Kenneth Zeitz, Jacob M. Geist, and Peter K. Lashrnet,

Allentown, 1 a, assignors to Air Products and Chemicals, Inc., a corporation of Delaware Filed Jan. 18, 1963, Ser. No. 252,359 5 Ciaims. (Ci. 62'7) The present invention relates to low temperature refrigeration, more particularly to methods for producing refrigeration at low temperature levels by the expansion of gas.

It is an object of the present invention to provide techniques for low temperature refrigeration that will achieve quite low temperature levels.

Another object of the invention is the provision of low temperature refrigeration techniques that produce a maximum of refrigeration with a maximum expenditure of energy.

Finally, it is an object of the present invention to provide low temperature refrigeration methods that will be simple and easy to practice.

Other objects and advantages of the present invention will become apparent from a consideration of the following description, taken in connection with the accompanying drawing, which is a diagrammatic flow sheeet of a low temperature refrigeration system according to the present invention.

Briefly stated, the present invention comprises the discovery that low temperature refrigeration is achieved with the concomitant achievement of the above objects by providing first and second streams of compressed gas, expanding a first portion of the first stream, cooling the second stream by heat exchange with said expanded first portion, expanding a second portion of the first stream, further cooling the second stream by heat exchange with said expanded second portion, and expanding the further cooled second stream. In its more preferred forms, the invention is characterized in that the second portion is cooled by heat exchange with the expanded first portion prior to expansion of the second portion, the pressure of the first stream before expansion is substantially greater than the pressure of the second stream before expansion, the pressure of the first stream after expansion is substantially greater than the pressure of the second stream after expansion, the first and second portions constitute the whole of the first stream, the first and second portions are expanded isentropically and the second stream is expanded adiabatically, and both streams are helium.

Referring now to the drawing in greater detail, there is shown a low temperature refrigeration system in which two streams of normally gaseous material move in closed cycles and in heat-exchange relationship with each other. The first stream is compressed by a compressor 1 and discharged at an elevated pressure to a conduit 3, through which it passes through heat exchanger 5. A branch conduit 7 oil conduit 3 downstream from exchanger 5 removes a portion of the stream in conduit 3 and passes it to an expansion engine 9 in which the branch stream is expanded with work and cooled. The expanded branch stream in conduit 7 then passes through a heat exchanger 11 in which it is warmed in heat-exchange relationship with the other stream, and thence passes to a return conduit 13 in which it passes through heat exchanger 15 in heatexchange relationship with the remainder of the ma terial passing through conduit 3, and then through heat exchanger 5 in which it is warmed in heat exchange with the compressor output, and then to the intake of compressor 1.

The remainder of the material in conduit 3 passes through heat exchanger 15 and through a further heat exchanger 17 and is then expanded with work in an expansion engine 19 in which it is cooled, and then passes through heat exchanger 21 in which it is warmed against the other stream. It then passes through heat exchanger 17 on its way back to compressor 1 through conduit 13, then through heat exchangers 15 and 5 to the intake of compressor 1. This remaining material is thus heat exchanged with itself before and after expansion, in heat exchanger 17, and constitutes the entire balance of the stream in this first closed cycle.

The other or second closed cycle stream, whose volume of flow is only a minor proportion of the how of the first stream, leaves compressor 23 at elevated pressure and passes through conduit 25 and heat exchanger 27 and thence through exchanger 11 in countercurrent with the stream in conduit 7. This material in the second cycle then passes through exchanger 2? and through exchanger 21, and then to an exchanger 31 in which the second stream is exchanged with itself before and after expansion.

Expansion and partial liquefaction of this second closed cycle gas is effected through an expansion valve 33, whence the cooled and expanded and partially liquefied stream passes in heat-exchange relationship through a device to be cooled, designated at 35, when it returns through return conduit 37 through exchangers 31, 29 and 27, in that order, and thence to the intake of compressor 23.

As an illustrative example of the operation of a system according to the present invention, let it be assumed that the fiuid in both closed cycles is helium. The helium in this illustrative example is compressed in compressor 1 to 353 pounds per square inch absolute (p.s.i.a.) and enters exchanger 5 at 160 F. It leaves exchanger 5 at 300 F. and a pressure of 331 p.s.i.a. The side stream withdrawn through conduit 7 amounts to 36% of the whole and is expanded in expansion engine 9 to a pressure of 35.5 p.s.i.a. and a temperature of -353 F. In exchanger 11, this side stream is warmed to 350 F. and returns through conduit 13 The remainder of the stream in conduit 3, amounting to about 64% of the original whole, is cooled in exchanger 15 to 328 F. and in exchanger 17 is further cooled to 436 F. It'is still further cooled in expansion engine 19 to 446 F. and falls to a pressure of 35.0 p.s.i.a. In exchanger 21, this expanded stream is slightly rewarrned, to 44S F. on its way to return conduit 13. In return conduit-13, the returning material is warmed in exchanger 17 to 33l F., in exchanger 15 to 312 F., and in exchanger 5 to F. whereupon it re-enters compressor 1 at a pressure which, because of frictional pressure drops in the system, is now 33.5 p.s.i.a.

On the other or second side, that is, in connection with the second closed cycle helium that passes in circuit between compressor 23 and device 35, the working fluid is of much smaller volume than in the cycle previously described, and in the described embodiment amounts to only 5% of the fluid on the other side. This stream leaves compressor 23 at a pressure of 78.5 p.s.i.a. at a temperature of F., and leaves exchanger 27 at 331 F. It

3 is cooled in exchanger 11 to 352 F. and in exchanger 29 to -436 F. It is further cooled in exchanger 21 to -445 F, and in exchanger 31 to 450.5 F. Conduit friction has by this time reduced the pressure to 75.0 p.s.1.a.

Through expansion'valve 33, the pressure of the material in stream 2-5 is reduced to 1.5 p.s.i.a. and the temperature falls to 455.2 E, at which time, under equilibrium conditions, it is mostly in liquid phase and partly in vapor phase. Actually, of course, the inherent inefficiency of expansion valve 33 prevents equilibrium conditions of liquefaction from being quite achieved.

The partly liquefied helium cools device 35 with concomitant at least partial vaporization of the liquefied helium, and leaves device 35 under the same conditions of temperature and pressure and is warmed in exchanger 31 to a temperature of -446 F, in exchanger 29 to -357 F., and in exchanger 27 to 151 B, after which it enters the suction side of compressor 23 and is recompressed to repeat the cycle. 7

An important feature of the invention is the fact that two compressors in two completely different circuits permit different modes of operation to meet specific circumstances. Moreover, if the'expansion engines of the first circuit were obliged to, expand all the working fluid to the pressure of the other circuit, for example to 1.5 p.s.i.a., then the expansion equipment would have to be enormous in size.

From a consideration of the foregoing disclosure, it will be .obviousthat all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand.

Such modifications and variations are considered to be within the purview and scope of thepresent invention as defined by the appended claims.

What is claimed is:

1. A low temperature process for refrigerating a device to be cooled comprising the steps of compressing and expandingafirst gas in a closed cycle in which the compressed first gas is expanded in a plurality of work expansion steps at progressively decreasing temperature levels and in which effiuent from the work expansion steps is passed in heat interchange with compressed first gas to cool compressed first gas prior to-the work expansion step, compressing a second gas,

passing compressed second gas successively in heat interchange with effluent of the work expansion steps at the progressively decreasing temperature levels to cool compressed second gas to a low temperature, expanding in a valve, cool compressed second gas to effect at least partial liquefaction of the second gas, passing expanded second gas in heatinterchange with the device to be cooled, i and passing second gas following the last-named heat interchange in countercurrentheat interchange with compressed second gas following the aforementioned heat interchange between compressed second gas and efiiuent of the work expansion steps,

. the compressed second gas being passedin heat interchange with efiluent of the Work expansion steps prior to the heat interchange between the. efiluent of the work expansion steps and the compressed first gas.

2. A low temperature process for refrigerating a device to be cooled comprising the steps of compressing a first gas,

expanding a first portion of the compressed first gas by a first work expansion step at a first temperature level,

expanding a second portion of the compressed first gas 4 by a second work expansion step at a second temperature level lower than the first temperature level, passing the second portion of the compressed first gas successively in heat interchange with efiluent of the first and the second work expansion step prior to the second work expansion step, compressing a second gas, 7 passing compresseclsecond gas successively in heat interchange with effluent of the first work expansion step and the second work expansion step to cool compressed second gas to a low temperature, expanding in a valve, cool compressed second gas to effect at least partial liquefaction of the second gas, passing expanded second gas in heat interchange with the device to be cooled, Y and passing second gas following the last-named heat interchange successively in countercurrent heat interchange with compressed second gas following the aforementioned heat interchange between compressed second gas and effluent of the first and second work expansion steps, j I the compressed'second gas being passed in heat interchange with efiluent of the first and second work expansion steps prior to the heat interchange between the efiiuent of the first and second work expansion steps and the compressed first gas. 3. 'A low temperature process for refrigerating a device to be cooled as defined in claim 2 in which the first compressed gas is under a pressure substantially greater than the pressure of the second compressed gas.

4-. A low temperature process for refrigeratinga device to be cooled as defined in claim 2 in which the pressure of the effiuent of the second expansion step is substantially greater than the pressure of the expanded second gas.

5. A low temperature refrigeration process, which proc: ess comprises the continuous steps of (a) compressing first and second streams of gas in first and second compressing Zone;

(b) cooling the firt compressed stream of gas by indirect heat exchange with expanded first stream gas;

(c) dividing the resultant cooled first compressed gas stream into a first portion and second portion;

(d) expanding the first portion of said first stream,

I thereby cooling said first portion;

(e) passing the resultant cooled first portion in heat exchange with the second compressed stream, thereby cooling said second compressed stream;

(f) passing the-heat exchanged cooled first portion from step (e) into heat exchange with the second portion, thereby cooling said second portion;

( g) further cooling the resultant cooled second portion by heat exchange with the expanded second portion;

(h) expanding the further cooled second portion, thereby lowering its temperature;

(i) further cooling said cooled second compressed stream from step'(e) by heat exchange with the low temperature expanded second portion of step (h);

(k) utilizing the heat exchanged low temperature expanded second portion of step (h) as the expanded second portion of step g) (l) additionally cooling the second portion in step (f) with the heat exchanged expanded second portion from step (k); t V A (m).utilizing the expanded first and second portions from steps (f) and (l) as the expanded first stream gas of step (b); 1

(n) recycling the heat exchanged expanded first stream .gas from step (m) to said first compressing zone;

(0) expanding the furthercooled second compressed stream, thereby cooling said stream to a low temperature; r r

(p) heat exchanging the very low temperature expanded second stream with a Warmer body, thereby utiliz- 5 6 ing refrigerant value of the very low temperature References Cited by the Examiner second stream; (q) heat exchanging the resultant utilized low temper- UNITED STATES PATENTS ature stream of step (p) with warmer temperature 8 ,052 2/ 14 Aumont 6Z-40 streams of itself three times as follows: 5

( 1) with said further cooled second compressed FOREIGN PATENTS Stream Preceding expansion p 882,211 11/61 Great Britain. (2) with said cooled second compressed stream 499 9 2 5 Italy.

preceding cooling step (i), and (3) with said second compressed stream preced- 10 ROBERT A. OLEARY, Primary Examiner.

ing cooling step (e); and (r) recycling the resultant stream from step (q) to MEYER PERLIN, Examiner.

the second compressing zone.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,199,304 August 10, 1965 Kenneth Zeitz et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 3, line 56 and column 4, line 12, for "valve," each occurrence, read valve line 39, for "zone" read zones line 40, for "firt" read first Signed and sealed this 24th day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A LOW TEMPERATURE PROCESS FOR REFRIGERATING A DEVICE TO BE COOLED COMPRISING THE STEPS OF COMPRESSING AND EXPANDING A FIRST GAS IN A CLOSED CYCLE IN WHICH THE COMPRESSED FIRST GAS IN A CLOSED CYCLE PLURALITY OF WORK EXPANSION STEPS AT PROGRESSIVELY DECREASING TEMPERATURE LEVELS AND IN WHICH EFFLUENT FROM THE WORK EXPANSION STEPS IS PASSED IN HEAT INTERCHANGE WITH COMPRESSED FIRST GAS TO COOL COMPRESSED FIRST GAS PRIOR TO THE WORK EXPANSION STEP, COMPRESSING A SECOND GAS, PASSING COMPRESSED SECOND GAS SUCCESSIVELY IN HEAT INTERCHANGE WITH EFFLUENT OF THE WORK EXPANSION STEPS AT THE PROGRESSIVELY DECREASING TEMPERATURE LEVELS TO COOL COMPRESSED SECOND GAS TO A LOW TEMPERATURE, EXPANDING IN A VALVE COOL COMPRESSED SECOND GAS TO EFFECT AT LEAST PARTIAL LIQUEFACTION OF THE SECOND GAS, PASSING EXPANDED SECOND GAS IN HEAT INTERCHANGE WITH THE DEVICE TO BE COOLED, AND PASSING SECOND GAS FOLLOWING THE LAST-NAMED HEAT INTERCHANGE IN COUNTERCURRENT HEAT INTERCHANGE WITH COMPRESSED SECOND GAS FOLLOWING THE AFOREMENTIONED HEAT INTERCHANGE BETWEEN COMPRESSED SECOND GAS AND EFFLUENT OF THE WORK EXPANSION STEPS, THE COMPRESSED SECOND GAS BEING PASSED IN HEAT INTERCHANGE WITH EFFLUENT OF THE WORK EXPANSION STEPS PRIOR TO THE HEAT INTERCHANGE BETWEEN THE EFFLUENT OF THE WORK EXPANSION STEPS AND THE COMPRESSED FIRST GAS. 